2007 Saturn Aura XR: Fuel Economy

The last Camry I drove did the same thing but that's been a year or two now. I drove from Long Beach, Ca. to Willow Springs Raceway in Rosamond Ca. Nissan Altima doesn't have the same problem but the Hyundai Azera did.
 
I probably was driving 70-75 most of the way. I just set the cruise control and let it do what it was gonna do.
 
Steep hills, no problem - the gradual ones really seemed to rub the transmission the wrong way.

We keep hearing how the GM automatics are tuned for maximum efficiency, yet they still deliver economy on the lower end of their class. What gives?

1) The 3.6 has never been the most fuel efficient engine. It develops good power, has a lot of torque, and is smooth, but maybe is not as efficient as possibly the 3.5 from Toyota.
 
2) The torque peak for the 3.6 is at 3200 rpm, I believe, but 70-75 mph is around 1600-1800 rpm in top gear.
 
Thanks for the response. What you described is why for most hills I use the slingshot approach. I personally hate having the cruise control on climbing hills. Every car I have ever riden in with the cruise control on does the transmission hunt, no matter what type of car or truck. Cruise control is fine on flat ground, no good in the mountains.
 
The Altima has the CVT, correct?

AuraKR:
 
Agree 100% on cruise control on hills. It's just not as adaptive as one's own leg/foot.
 
Also, yes, our Altima has the CVT.
 
-mike

It appears many of the 6 speed automatics have that problem with gradual inclines. Some also appear to have an issue with downshifting. Have you guys driven the Mercedes 7 speed automatic or the Lexus 8 speed automatic? How are they in comparison?

aurakr, I have a 2007 S550 with the 7-speed and whenever I go on long drives I just set the adaptive cruise control and leave it for hours on end. The car absolutely always chooses the correct gear. It is so strange, you start to go up a hill and the car keeps full power all the way to top regardless of grade. The shifts are seemless and the transmission never "hunts"
 
On the same note, the 7-speed is a "learning" transmission so the car begins to adapt to your driving style. I have had the car for almost two years now and the transmission has completely adapted to me and is ludicrously smooth and suprisingly fuel efficient. (I average around 19-20mpg in mixed driving consistently). When I first got the car, however, the transmission was a little busy at times.

mercedesfan
 
Thanks for the response. I was curious. I know the XR transmission is also a learning transmission. For the first 1000 miles, mine did what you described as well, then became butter smooth.
 
It might be that GM has been a little aggressive with the software for fuel economy. What rpm are you at 60-70-80 mph? Do you have a V8? Just trying to get a feel for the gear ratios with Mercedes.

Aurakr,
 
it's a 2007 Mercedes-Benz S550.
Obviously it has a V8.
lol.

S550 has a 381hp 5.5L V8.
 
AuraKR, I wonder why GM chooses to have the torque peak "so low" in the RPM range? GM should tinker with the VVT and maybe use a variable intake manifold to better spread the torque over the entire RPM range. Its still a nice V6 BTW! Id like to see a dyno plot of the 3.6 and the DI 3.6 to really get a feel of the power/torque under the curve. Really nice V6 BTW!
 
As you know Honda V6's usually hit their torque peak in the 5000 RPM range and then taper off while still offering 85-90% of torque under 2000RPM at least this is what the dyno plots say. If Honda would only implement a 6AT instead of the wide ratio 5AT it would also help acceleration and economy.

hondacura4
 
You may have something there. I'm not sure why Honda hasn't come out with a 6 speed auto as of yet. Have you heard on them working on any? My own gut feeling is that part of the issue on gradual inclines is the aggressiveness of the software to try to maximize economy. I have heard that new software updates are out there and some claim it makes a huge difference and some claim it hasn't affected the mileage either.
 
Thanks for the info on the 550. I'll admit I am not as up to date on Mercedes as I should be for the blogs. That his S550 averages 19-20 mpg in overall driving is excellent.
 
All in all, I am really curious to see what the VCM does for the Accord's mileage. As I stated before, I wish the 3.6 had cylinder deactivation.
I expect it will be a couple of years before the XR sees the DI version of the 3.6, if ever :(

In the Malibu road test second opinion the author states he got 26mpg on a long road trip back to the Edmunds office. 21.4mpg is pretty low for a highway trip.
 
The other reason the Aura doesnt match camry in fuel economy is weight. The epsilon cars are amongst the heaviest in this class. I believe the Camry is about 200lbs lighter.

aurakr, I should know the response to your question right away but I don't pay that much attention. I do know for a fact, however, that between 70 and 80mph on the highway my S550 is right around 2000 rpm. That is part of the reason the car is so quiet at highway speeds.
 
BTW, Another aspect to consider for gas mileage is aerodynamics. The S550 has an extremely low coefficient of drag right around .26 and I would wager some of the Aura's competitors are not far off of that. The Aura's blunt, aggressive nose undoubtedly hurts its overall coefficient of drag.

mercedesfan
 
.26, now that is amazing. I have yet to see a drag co-efficient for the Aura. I agree it would not be that good. I am just curious, is all.
 
1487
 
You are right about the weight. The first trip for Edmunds in the Accord yielded 22 mpg. The Accord weighs nearly the same as the XR. The Accord will probably have a lower drag co-efficient.
 
For the record, my XR has been on two road trips. Mileage from San Diego to Las Vegas and back was 26-28 mpg with speeds from 70-80 normally, with some bursts up to 90, all with the a/c on all the way. My wife and daughter went from San Diego to Huntington Beach and back, 70-90 mph and got around 26 mpg.

At the risk of jinxing it, I have to say this is the most civil Aura blog entry I have seen in a long time. Cool.

Weight is usually more of a factor in city fuel economy, because so much energy (hence fuel) must go into accelerating the vehicle's mass. At a steady speed, aerodynamics and friction are more determinative.
 
Some big American sedans with tall gearing and big engines (high torque at low RPM) often do better than expected in fuel economy. I've posted previously about my MIL's LeSabre, which routinely gets 27-28 mpg at 75 mph, comparable to my much lighter Accord 3.0. I suspect GM kept the torque curve fat at the low end of the tach in order to minimize the need for downshifts--but it doesn't seem to have worked on the Aura XR in Edmunds' possession, probably because 3200 rpm isn't really that low. The gearing of the XR seems about right for the old 3.8 pushrod Buick motor, but very wrong for the 3.6.

as stated earlier, not vehicle with the 3.6 gets great mileage. I'm not sure how much the tranny has to do with it. The Lacrosse has the same engine and got 19/27 under the old standards with a 4 speed auto. The 3.6 was designed for torque with efficiency as a lesser priority. If Honda didnt have VCM their 3.5 would be no better as evidenced by the mileage on the V6 coupe.

I have heard from other XR owners that mileage keeps improving on these engines, sometimes up to 10,000 miles. The 3.6 is a very tight engine. I bought mine fully expecting to get the mileage I get. I doubt if I will ever exceed 28 mpg on a trip.
 
I am curious to see if the DI version will get better mileage, one because it makes far more power, 304 vs 252. But as stated before, I don't know if or when GM may put the DI in the XR. What I am waiting to see is the mileage improvement with the Vue with the 3.6 two-mode. I would love to see a 3.6 two-mode in the Aura XR.

I believe that after the Aura's road trip, the overall fuel economy was raised to 21.4

briancam
 
You are truly a genius. Duhhh. I think that you are correct, sir.
 
I forgot that the DIC does average over time. Good call.

I wasn't even considering the Aura XE with the 4-speed auto -- until I test-drove the XR. I found the 6-spd auto shifting to be a bit busy (while understanding that the shift logic would adapt somewhat to my driving over time). By comparison, the 4-spd in the XE was far smoother than I expected...probably because GM has had about 20 years to perfect it! After driving the XE, the tranny was no longer a dealbreaker (nor was the 3.5 pushrod), and I happily bought one.
 
My combined mileage in the XE is 22.5. IIRC, that's the exact combined mileage that was reported in Edmunds' Malibu review. Granted, that's about 70/30 freeway/street driving in my daily commute. On a road trip from LA to Santa Fe, NM, my highway mileage was as high as 30, and my city driving has never gone below 19.
 
Back to the Malibu review, one thing that surprised me was the comment about mediocre rear legroom. I find the Aura's rear legroom to be cavernous, so am I just biased, or does the Malibu (on the exact same platform) really have less legroom?

misterfusion
 
I have always wondered how the 3.5 feels in the Aura. I had an 2006 Impala LS with the 3.5 and averaged 24 mpg overall. I always liked the 3.5 and wondered how it would perform with a 6 speed. I know the Aura with the 3.5 has plenty of power, 0-60 in 7.7 seconds. I wonder if an Aura with the 3.5 and a 6 speed might be just the ticket for both mileage and performance for most people.
 
I too think the Aura has plenty of rear seat room. However most complaints have been more about the narrowness of the car. The only other midsize I have sat in was a 2007 Camry, and for some reason I thought it was lacking rear seat headroom.

stovt001,
 
Well you just jinxed it. The Aura sucks. The Camry is a better buy anyway you look at it.
 
---just wait for the responses---

Merc Fan,
 
How's your experience with the dealer? Back in the 90s I heard some very negatives remarks from Mercedes owners about the poor service quality. Some folks say that's what gave Lexus the room to push into the market aggressively (and I heard Lexus stole customer list from Mercedes but who knows if that really happened).

I agree that the legroom is more than adequate in the Aura. I was confused by the comments in the Malibu test about lack of rear seat space.

"If Honda didnt have VCM their 3.5 would be no better as evidenced by the mileage on the V6 coupe."
 
1487, Im not so sure about that. The gearing on the Accord V6 6 speed manual coupe is far tighter than the Honda V6 5AT. The Accord V6 5AT coupe is VCM equipped too.
 
My Acura CL-S has a similar drive train as the Accord V6 6MT. 3.2 SOHC VTEC V6 6MT, 260hp/238lbft of torque and I can actually use 6th gear going up moderate grades at highway speeds. I consistently get around 26-27mpg on the highway and the car still hauls ass!

Aurakr,
 
Does the Aura have a manual shift function (either paddle shifters or on the console)? The reason I ask is because my wife and I bought a 2007 Honda Fit Sport with an automatic transmission and it comes with paddle shifters. There are rather steep hills on the long drive from our house to my in-laws, and I got tired of the Fit downshifting at even the slightest incline. So now on long trips I put the car into manual shift mode, shift up to 5th gear, set the cruise and it never downshifts on hills. The good thing is that gas mileage remains awesome. But you will lose speed on long or steep hill climbs. But that was an acceptable trade off for me.
 
Would you mind experimenting with your Aura to see if it behaves the same way on hills and let us know? I'm very curious to see if that might help solve the shift quirks.
 
Thanks.

"1487, Im not so sure about that. The gearing on the Accord V6 6 speed manual coupe is far tighter than the Honda V6 5AT. The Accord V6 5AT coupe is VCM equipped too. "
 
My point is that without VCm the Honda V6 gets about the same mileage as the GM V6. Manuals typically get 1-2mpg better mileage than their auto counterparts. If the Accord coupe V6 with the manual gets 17/25 it is likely the mileage would be slightly worse with an auto. If Honda hadn't made VCM standard the Accord's mileage would be amongst the worst in class.

Aurakr: I think the 3.5 was a great choice for the Aura base engine. It's got plenty of power for my needs, and as I said, the 4-spd auto is pretty smooth. The reliability should be outstanding, with the only question-mark being the new VVT system (did the Impala 3.5 have that?). In all fairness, I can't think of any engine that couldn't be improved by adding a couple more gears to the slushbox, but as I said, the XE 3.5/4AT is (was) a great entry-level package.
 
Although I hope that the addition of a base 4-cyl will boost the Aura's sales as intended, I doubt that I would enjoy driving it. The Ecotec is a smooth engine, but it's not exactly a fuel miser in the larger displacements. The Aura's weight combined with that 4-spd auto will result in a performance AND economy penalty, and IMO the prospective entry-level Aura owner would be better served all-around by the 3.5 V6.

http://media.gm.com/us/powertrain/en/product_services/2008/HPT%20Library/HFV6/2008_36L_LY7_Aura_sae.pdf
 
Use that link to see the torque curve of the 3.6L engine- and remember it's SAE certified. You'll see that the curve is extremely linear and there are more than 200 lbs-ft from idle to power peak. Horsepower and torque curves cross at 5252 rpm and as you can see, the torque stays consistant after this point courtesy of the variable intake and exhaust valve timing and a variable path intake manifold system. I'd be curious to see an Accord's 3.5L V6 torque curve.
 
It's important to note, the Honda V6 lacks continuously variable valve timing. It features a one time intake only valve lift & time changing event at a set RPM. It is limited by it's SOHC architecture which interestingly enough is what allows VCM to be implemented. Cylinder deactivation using a DOHC configuration is cost prohibitive
 
The 6T70-E can handle a maximum of 280 lbs-ft of torque which is clear of the 273 lbs-ft that the DI version produces so I guess there is always a possibility of a Red Line but I doubt this do to cost considerations of the DI hardware. DI yields a 3% improvement in the fuel mileage over the port injected version which is really not enough to affect the EPA mileage. There is also the taboo of putting 300+ horsepower through FWD to consider as well.

"It's important to note, the Honda V6 lacks continuously variable valve timing. It features a one time intake only valve lift & time changing event at a set RPM. It is limited by it's SOHC architecture which interestingly enough is what allows VCM to be implemented. Cylinder deactivation using a DOHC configuration is cost prohibitive."
 
Chavis, as a die hard Honda enthusiast Im pretty aware of most technical aspects of Honda V6's as I own one, a 2003 260hp/232lbft Acura CL-S 6MT. Honda uses the SOHC VTEC approach because its cheaper, simpler, lighter, more compact and is less complex than a DOHC configuration. And yes, the "fixed VTEC' is just that fixed. These engines also use a variable intake design to flatten out the torque curve along with the VTEC itself. The best part is that Honda gets comparible or better numbers using this simple setup rather than going FULL BOAT DOHC dual VVT. So I dont think the Honda SOHC configuration is as "limited" as you say. It puts out pretty good power to be "limted" while using nearly 11 year old architecture as the Honda J series V6 debuted in the 1997 Acura CL 3.0 as the J30.
 
I dont know much about the VVT used in the GM DOHC 3.6 but I believe you stated it uses VVT on the intake AND exhaust valves correct? Does it have valve LIFT also like the VTEC system?
 
The only 2008 Accord V6 dyno plot I could find is from a V6 6MT coupe. I looked for a 08 VCM V6 dyno plot with no luck.
 

Chavis here is a 08 Honda Accord V6 6MT vs 07 Acura TL-Type S 6MT dyno plot. The only difference between the 2 V6's is compression ratio and a few other small things.
 
The second plot is comparing a 08 Accord V6 VCM 5AT (500 or so miles on the engine) vs 08 Accord V6 6MT. The VCM combined with the 5AT really sucks the life out of the V6 which doesnt have the performance benefits of the VTEC system. Honda could have done better here.
 
Remember when comparing the dyno Chavis provided to the 3 I provided, my plots measured HP at the wheels. Chavis' plot is at the crank not to the wheels.

Yes, the 3.6L has cam phasing on all four camshafts with no variable lift.
  
I used the word limited because there is a ceiling that Honda's SOHC design will reach because of the increased weight of modern cars. Variable cam phasing along with variable intake manifolds work to fatten the lower end of the rev range and produce more torque off idle which is becoming increasingly important as most of these sedans are 3400lbs and up. Since horsepower is the rate at which torque is applied, Honda enables its engines to rev quickly and reach higher rpms where they make plenty of power and breathe efficiently. So, even though honda engines typically don't make as much torque as the competition, they apply it at a faster rate. This approach works when you're lugging around a lightweight car but things change when the weight is up. The MDX is a perfect example of this. Despite its sky high compression ratio and increased displacement, the engine doesn't it move it off the line with authority though part of this may be due to tall gearing.
  
In fairness, I think the VCM hardware keeps the engine for revving as hard as the non VCM version of the engine which may help explain the plots you provided.
 
Honda's K series i-VTEC I-4s have adopted the more common design of continiously variable valve timing (intake only) in addition to the unique two stage lift and duration cam profiles. I wouldn't doubt Honda's next V6s will be of a more modern DOHC configuration.

3 reasons the MDX doesn't shoot off the line: (1)The stall on Honda 5ATs simply sucks ! (2) The 5ATs gear ratios are waaaay to wide. (3) For some reason Acura chose high end HP over more low end which is kind of odd given the MDX isn't a light vehicle like you stated. This 3.7 engine really shines in the middle to upper rev ranges. The "lack" of low end could be improved with a more aggressive stall and 6AT. So I do agree with you to a point regarding a more modern VVT/VTEC system would be in order for future higher powered applications. The 3.7 still puts out some good numbers 300hp and 275lbft more than even GMs 4.2 DOHC inline 6.
 
I doubt Honda would go with a DOHC V6 with the next generation V6 as I think there is a lot of life left in a NEW SOHC configuration especially with the upcoming next generation a-VTEC system.
 
A true DOHC i-VTEC V6 configuration similar to the system on the high performance K series would put out some serious HP/TQ (think Porsche GT3 HP/TQ numbers). Id truly like to see that in a high powered configuration (350hp-400+) but the DOHC i-VTEC isn't necessary for the current models as it would be overkill.
 
The wonderful K -series! Well you were correct to a point. The DOHC 2.4L in the Accord, CRV, Element all have i-VTEC. i-VTEC in this application is intake only VVT/lift with intake only variable cam phasing). These have more of a maximum efficiency based setup.
 
Now the high performance versions of the K are a bit different. They rev higher, have high compression, stronger internals, big cams ETC ETC. These versions are available in the TSX (2.4L) and the Civic Si (2.0). They implement DOHC i-VTEC also with variable cam phasing only on the intake valves but the VVT and lift are on BOTH the intake and exhaust valves which gives them that surge of power and a flat torque curve that continues to the high red line. Ive personally witnessed an 06 Civic Si 2.0 with a race header, hi/po cat, full exhaust, and Hondata K-PRO (standalone ECU) put out 247hp and 175lbft of torque TO THE WHEELS with NO internal modifications. Pretty impressive for a internally stock 2.0L engine.

"These engines also use a variable intake design to flatten out the torque curve along with the VTEC itself. The best part is that Honda gets comparible or better numbers using this simple setup rather than going FULL BOAT DOHC dual VVT. "
 
The numbers are there but when you compare the Accords acceleration to the less powerful (and slightly heavier) Aura and Malibu you begin to see some of the limitations. I'm sure SOHC is cheaper and this is why Honda has stuck with this design for so long but you have to admit the pressure is building to go DOHC since every major competitor has already done so. Also, I'm pretty sure that almost every competing 3.5L V6 has dual stepless VVT like the GM V6 although most do not have variable lift as far as I know.
 
GM's 4.2L is only slightly behind the Acura 3.7 V6 in hp (has more torque with 277 lb ft) and has been around for 5 years. It also only has VVT on the exhaust valves.

Well since Honda doesn't want to introduce a six speed auto, they need to make their engines in heavier vehicles more flexible at lower revs.
 
The performance versions of the K also have 3 cam profiles per cylinder instead of 2.
 
I'm well versed in Honda engine tech but fundamentally, I just don't agree with their philosophy. Not to take anything away from them but I'm just more of a torque person.

"The numbers are there but when you compare the Accords acceleration to the less powerful (and slightly heavier) Aura and Malibu you begin to see some of the limitations. I'm sure SOHC is cheaper and this is why Honda has stuck with this design for so long but you have to admit the pressure is building to go DOHC since every major competitor has already done so. Also, I'm pretty sure that almost every competing 3.5L V6 has dual stepless VVT like the GM V6 although most do not have variable lift as far as I know."
 
1487, you must not have looked at the dyno plots that were provided above as the Accord VCM puts out MUCH less power to the wheels than the non VCM Accord V6 6MT. Im willing to bet that the Aura/Malibu actually make more power to the wheels than the Honda VCM V6. Id say the GM 3.6 VVT DOHC V6 puts out roughly 210-215hp and 205-210lbft of torque to the wheels which would put it above the Accord VCM V6 which put down 211hp and a embarrasingly horrible 189lbft of torque to the wheels, thats about a 25% drivetrain loss!
 
On that note the Aura/Malibu still have most of the advantges: more displacement, 6AT, more torque, dual VVT, variable cam phasing, variable intake design and a DOHC configuration. Weight is a small advantage for the Accord V6 EX-L sedan as it only wieghs about 35-50lbs less than the Aura and Malibu.. Considering all these advantages the Malibu still ONLY runs beside the Accord VCM V6 (going by Edmunds earlier statements) while the Accord uses a much "less advanced" valve train configuration.
 
Please explain to the benefits of using the 3.6s engine technology as the Accord pretty much offers the similar performance with a much simpler design. Why have all this technology if your not going to use its full potential? That could be said for other DOHC VVT V6s in the same segment also. As of now the best V6 in the segment would be the Toyota as it provides great economy and performance in one package.

"Please explain to the benefits of using the 3.6s engine technology as the Accord pretty much offers the similar performance with a much simpler design. Why have all this technology if your not going to use its full potential? That could be said for other DOHC VVT V6s in the same segment also. As of now the best V6 in the segment would be the Toyota as it provides great economy and performance in one package."
  
Good point but you have to remember that this engine will be used in a myriad of applications, just the like the J series V6. As a stated earlier, IMO the J's VTEC approach is not as successful in heavier vehicles. If you look at the weight of GM's crossoverss, the fact that this engine can move them smartly with the same amount of torque as the Malibu impresses me. Now granted, 0-60 in ~ 8-8.2 secs is not breath taking but when you consider the 4800-5000 lbs curb weights you would have to admit it is at least respectable. Even though the SUVs have a high output version of the 3.6L that breathes better at high rpms, the torque curves are pretty much identical. The 3.6L in the upcoming G8 makes peak torque at 2100rpm and stays within 10 lbs-ft of that until after 4000 rpm. That bottom heavy pull is what draws me to this engine and overall, I think it's a more flexible solution than the Honda V6 for a wide range of vehicles.
 
I do agree that the Toyota V6 is the one to beat.